The present invention relates to a piston ring for use in an internal combustion engine having a piston and a cylinder whose cross sectional shapes are an ellipse or an oblong circle.
In one type of internal combustion engine, engine cylinders and pistons are formed into an elliptical or elongated circular shape in cross section with the intention of reducing the total length of a multi-cylinder engine and increasing the opening areas of intake valves and exhaust valves. Japanese utility model provisional (un-examined) publication Sho No. 54-161410 discloses a piston ring for internal combustion engines of this kind. This piston ring is in a single piece and has a ring gap joint near the minor axis of the elliptical ring shape. This piston ring is mounted around a piston by broadening the ring gap so wide that it is often damaged or plastically deformed. Furthermore, this piston ring can not provide sufficient pressure against the cylinder wall at the portions of a rectilinear shape or a gradual curve near the ends of the minor axis.